A large number of light duty production machines, including food processing, material handling, conveying, packaging machines, etc., use relatively simple and reliable AC motors having a fixed 1800 RPM, nominal, output speed. A typical, very popular motor, standardized as the National Electrical Manufacturers Association NEMA-56 frame size, is manufactured and sold by many manufacturers. Typically, the motor has a no load output of one speed only, based on the electrical cycle upon which it operates and its internal configuration. It is necessary to obtain usable output (rotational or translational), at speeds different from that of the motor, and in some cases at selectively different speeds.
It is known to provide a speed reducing gearbox which, through a series of gears interacting with the output shaft of the motor, provides a reduced speed, and in some cases selectively variable reduced speeds. A gearbox typically consists of a number of interactive gears of appropriately varying diameters and matched tooth pitch, and a housing to restrain translation of the gears while allowing them to rotate upon axles. In order to ensure smooth operation of the gears, it is necessary to lubricate them using oil or grease. It is also necessary to seal the housing so that the oil or grease lubrication does not leak out into the work environment, which may be in a food processing plant or other situation where stray lubricant would be undesirable.
Typically, it is possible to reduce the speed of rotation at each stage (i.e., across each gear pair) by no greater a degree than 1/5. Therefore, depending upon the relation between the output of the motor and the speed desired for the driven device, multiple stages might be required. For instance, the NEMA-56 referred to above operates at 1800 RPM. Typical applications require an input of no greater than 100 RPM, for instance stock feeders, conveyors, pallet wrappers, and food processing machines. Thus, a typical reduction would require two or more stages or four or more gears. Each additional stage requires accurately aligned bearings and a housing to carry the torque reaction to structure either through mounting brackets or a torque arm, depending upon whether the speed reducer is rigidly mounted (with shafts flexibly coupled) or floating on the input or output shaft (with the torque reaction passing to structure via a link pivot mounted at its ends between the structure and some point on the reducer housing offset from the shaft centerline (i.e. a torque arm)).
Standard gear reduction systems suffer from numerous additional drawbacks. The housings required to hold the gear train in place while each of the gear elements rotates at a high rate of speed are heavy, expensive and large. The housing must securely contain the necessary grease or other lubricant within it. The gear system is noisy and produces high vibrations at various frequencies. Maintenance cost and time are rather high, due to deterioration of the various rolling surfaces, degradation of the lubricant and wasted energy due to heating. Further, because the gears rotate at high rates of speed, during maintenance or other times when the housing is removed, they can present a serious hazard to workers in the vicinity.
Thus, the several objects of the invention include providing a means for reducing or enhancing the speed of a rotary shaft while: eliminating lubricants and their leaks; eliminating excess weight, such as heavy sealed casings, gears and bearing housings; eliminating mounting brackets and torque arms; eliminating shaft couplings and alignment problems; eliminating maintenance adjustments for wear; reducing the space occupied by the drive package; improving the safety conditions under which the machine can be operated; reducing the number of moving parts; reducing the number of different types of parts; minimizing risk of destruction of the drive upon overload; accomplishing all of the foregoing with a fully reversible capability; and providing for variable degrees of speed reduction. These and other objects of the invention will be evident to one of ordinary skill in the art with reference to the following description and figures of the drawing.